1. Field of the Invention
This invention relates to a process for growing a crystal to be used in, for example, electronic devices, optical devices, magnetic devices, piezoelectric devices or surface acoustic devices such as semiconductor integrated circuit, optical integrated circuit, magnetic circuit, etc. Particularly, it pertains to a growth method of a crystal to be used suitably for formation of solar battery, etc.
2. Related Background Art
In the prior art, in solar batteries, package MOS transistors, etc., there have been invented devices of the SOI structure of the mode forming an insulating film on a metal, forming an opening at a part of the insulating film and making contact with the metal surface exposed from the opening.
However, for forming a high performance device by use of the above-mentioned mode, the technique for forming a monocrystal of a semiconductor on the insulating film in contact partially with the metal surface and the technique for making sufficient ohmic contact at the interface between the metal and the semiconductor are demanded. One which has made it substantially realizable is the selective nucleation method developed separately by the Applicant of the present application, as disclosed in Japanese Laid-open Patent Application No. 63-107016, EP 244081A1. The selective nucleation method proposed by the present Applicant is inclusive of the technique of generating a nucleus which can become a monocrystal by growing on a fine metal surface by the gas phase method, and growing a crystal from the nucleus of said crystal.
However, according to this method, since the method of generating a nucleus of a semiconductor monocrystal on a fine metal surface by the gas phase method and growing a crystal from the nucleus of said crystal, it was sometimes difficult to form a crystal containing an impurity at high concentration depending on the formation conditions. Therefore, in some cases, the ohmic contact between the metal and the semiconductor surface may be insufficient.
Also, there is an Si wafer in which an impurity is diffused into the back surface, then a metal is deposited by sputtering vapor deposition, etc. to form an electrode, as used in constituting the most basic solar battery. However, in this constitution, process treatments must be applied on both the front and back surfaces of the device, and additionally an Si wafer is used. Therefore, the shape and the size of the device are necessarily restricted, whereby the cost is high, as well as involving technical difficulty, and such technique was extremely disadvantageous in enlargement of area.
As described above, in the so-called SOI structure having a semiconductor film provided on an insulating film having a contact hole (opening) on a lower electrode, there is involved the problem in utilization of a monocrystal having good electrical contact with the lower electrode, and also when employing a wafer, there are involved problems with respect to reduction of cost, simplification of the steps and enlargement of area, whereby there remained tasks for achieving higher performance and practical application of the device.